The present invention relates to photolithography systems and methods, specifically, to devices and methods for creating 2-D and 3-D patterns on substrates without the use of a mask.
Photolithography systems are known in the art that direct light beams onto a photosensitive surface covered by a mask, etching a desired pattern on the substrate corresponding to the void areas of the mask. Maskless photolithography systems are also known in the art as described in Singh-Gasson, Sangeet et al., Nature Biotechnology 17,974-78, 1999. The system described in this article uses an off-axis light source coupled with a digital micromirror array to fabricate DNA chips containing probes for genes or other solid phase combinatorial chemistry to be performed in high-density microarrays.
A number of patents also exist which relate to maskless photolithography systems, including U.S. Pat. Nos. 5,870,176; 6,060,224; 6,177,980; and 6,251,550; all of which are incorporated herein by reference. While the previously described maskless photolithography systems address several of the problems associated with mask based photolithography systems, such as distortion and uniformity of images, problems still arise. Notably, in environments requiring rapid prototyping and limited production quantities, the advantages of maskless systems as a result of efficiencies derived from quantities of scale are not realized. Further, prior art references lack the ability to provide rapid prototyping.
In particular, alignment of patterns with respect to target substrates in maskless systems can be problematic. Various solutions have been proposed to mitigate the effect of alignment problems, including the digital shifting of the projected mask pattern to compensate for misalignment of a substrate. However, this technique requires that the substrate be closely aligned initially and is better suited for high volume production runs which incorporate automatic initial alignment systems. In a rapid prototyping, limited quantity environment, automated means of initial alignment are not cost effective.
In addition, conventional maskless alignment systems are normally limited to coplanar, two-dimensional alignment. However, there is a need in the art to create three-dimensional patterns on substrates. Creating three-dimensional patterns requires further alignment of the substrates in a third dimension perpendicular to the two coplanar dimensions. In the third dimension, computerized shifting of the mask pattern cannot compensate for misalignments in a direction parallel with an incident light beam. As a result, an ability to align a substrate in a third dimension in a rapid prototyping, reconfigurable environment is needed.
Another problem with maskless photolithography systems is that the mask pattern image projected is formed by pixels, instead of continuous lines. As a result, gaps may exist between adjacent pixels, which, when projected on a substrate, may allow the area between the pixels to be exposed, resulting in a break in the imaged pattern. For example, if the desired pattern is a circuit, gaps may be inadvertently exposed and formed in a trace, resulting in an electrical gap. The exposure gaps caused by the pixel nature of the micromirror arrays, or pixellation, may cause open circuits or unwanted capacitive effects where trace width or thickness is critical.
Another problem with current art systems is the phenomenon of xe2x80x9cstiction,xe2x80x9d wherein the individual mirrors in a micromirror area tend to xe2x80x9cstickxe2x80x9d in a specific orientation if left in that position for an extended period. Consequently, a higher voltage needs to be applied to the mirror drive to point the mirror in another desired direction. Thus the micromirror array consumes more power than normal and affects the reliability of the mirror.
Accordingly, there is a need in the art for a method and system for maskless photolithography to provide a more effective way to fabricate custom devices in a low volume production environment. This system needs to combine ease of use, reconfigurability, and the ability to provide coarse manual alignment and automated fine alignment of mask patterns. In addition the system needs to address the exposure gaps inherent in the process due to the pixel nature of the projected mask and provide means for eliminating stiction. In summary, the system needs to provide all the advantages of a maskless photolithography system at a reasonable cost, and include capabilities tailored to direct writing in a rapid prototyping environment.
In view of the foregoing deficiencies of the prior art, it is an object of the present invention to provide a maskless photolithography system for creating 2-D and 3-D patterns on substrates.
It is another object of the present invention to provide an easy to use, reconfigurable, rapid prototyping maskless photolithography system.
It is still another object of the present invention to provide a directly coupled optical system for maskless photolithography that ensures efficient transfer of light energy to a substrate for performing photolithography.
It is yet another object of the present invention to provide a projected image for maskless photolithography that is free from distortion and uniform throughout out the exposure area.
It is still another object of the present invention to provide a positioning fixture, selectively movable in a three dimensions to accurately position a substrate for maskless photolithography.
It is another object of the present invention to provide a maskless photolithography for creating micro and macro three-dimensional structures.
To achieve these objects, a system and method are provided to create two dimensional and three dimensional structures using a maskless photolithography system that is directly reconfigurable and does not require masks, templates or stencils to create each of the planes or layers on a multi layer two-dimensional or three dimensional structure. In an embodiment, the invention uses a micromirror array comprising up to several million elements to modulate light onto a substrate that has photoreactive compounds applied to the exposed surface. The desired pattern is designed and stored using conventional computer aided drawing techniques and is used to control the positioning of the individual mirrors in the micromirror array to reflect the corresponding desired pattern. Light impinging on the array is reflected to or directed away from the substrate to create light and dark spots on the substrate according to the pattern. In addition, an alignment fixture, movable in three dimensions, for mounting of the substrate is provided. The alignment fixture allows the affixed substrate to be moved in three dimensions, providing alignment in two, coplanar dimensions and a third dimension perpendicular to the two coplanar dimensions. By providing alignment in the third dimensional direction, the invention advantageously provides the capability to produce three-dimensional structures on a substrate. Further, the positioning information provided to the micromirror array can be modulated to cause the individual mirrors to change their angular position during exposure to reduce the effects of pixelation and stiction.
The advantages of the invention are numerous. One significant advantage is the ability to use the invention as a reconfigurable, rapid prototyping tool for creating two-dimensional and three dimensional micro and macroscopic objects. Another advantage of the invention is that it provides the ability to reduce prototyping costs and enable devices to be fabricated more quickly with less risk. Yet another advantage of the invention is the ability to utilize different designs and operating conditions on a single device. A further advantage is the ability to use computer network to transfer designs across networks for immediate light exposure of a substrate. Still another advantage of the current invention is a reduction in cost for prototyping activities realized by the elimination of physical masks and the ability to create both positive and negative tone images using the same array. Yet another advantage of the current invention is that pattern generation can be performed optically without having to use expensive vacuum system required by conventional mask based photolithography. A particular advantage of the current invention is the ability to create three-dimensional devices using an alignment stage to selectively expose successive layers in a substrate. By modulating the movement of the micromirror arrays, the negative effects of pixelation and stiction of micromirrors is reduced.
By providing the ability to individually control the individual micromirrors of the mirror array, any arbitrary micro or macroscopic structure can easily and quickly be created in substrates such as polymers, metals, or ceramics. Patterns such as glasses, microfluidic networks, thin film devices, hybrid material devices, micro electromechanical machines (MEMs), photomasks and combinations of the above mentioned devices can be created using the reconfigurable, application specific photolithography system disclosed.
All patents, patent applications, provisional applications, and publications referred to or cited herein, or from which a claim for benefit of priority has been made, are incorporated herein by reference in their entirety to the extent they are not inconsistent with the explicit teachings of this specification.